Method and system for pressure harvesting for underwater unmanned vehicles

Abstract

An underwater vehicle includes systems for harvesting ambient hydrostatic pressure and storing the same as a gas pressure in a compressed gas system and as a water pressure in a pressurized electrolysis system. The gas pressure is used to perform mechanical work or to generate electrical power via a prime mover. The water pressure is used to release pressurized hydrogen and oxygen gases via electrolysis. The pressurized hydrogen and oxygen gases are used in a combustion chamber to generate propulsion power for the underwater vehicle.

1 . A method for harvesting ambient hydrostatic pressure in a compressed gas system in an underwater vehicle, said method comprising the steps of:
 pressurizing a gas in a first gas tank in the underwater vehicle using a high ambient hydrostatic pressure encountered by the underwater vehicle during a submerged state of the underwater vehicle within a water body;   transferring at least some of the pressurized gas from said first gas tank to a second gas tank in the underwater vehicle;   transferring at least some amount of the pressurized gas from said second gas tank to a prime mover in the underwater vehicle for performing mechanical work;   storing the gas expressed by said prime mover in a third gas tank in the underwater vehicle;   transferring at least some amount of the gas from said third gas tank to said first gas tank in the underwater vehicle using a low ambient hydrostatic pressure encountered by the underwater vehicle during the submerged state in the water body.   
     
     
         2 . The method of  claim 1 , wherein the pressurizing step comprises the step of actuating a first differential valve operatively coupled to the first gas tank and subjected to the ambient hydrostatic pressure, when the underwater vehicle is submerged in the water body, thereby subjecting the gas contained in the first gas tank to the ambient hydrostatic pressure. 
     
     
         3 . The method of  claim 1 , further comprising the step of depressurizing the first gas tank by subjecting the gas contained therein to an ambient hydrostatic pressure lower than the gas pressure in the first gas tank by actuating a second differential valve operatively coupled to the first gas tank and subjected to the ambient hydrostatic pressure. 
     
     
         4 . The method of  claim 3 , further comprising the step of depressurizing the third gas tank by actuating a first valve disposed between the third gas tank and the first gas tank when the ambient hydrostatic pressure is lower than the gas pressure in the third gas tank, thereby causing a transfer of at least some amount of gas from the third gas tank to the first gas tank. 
     
     
         5 . The method of  claim 1 , further comprising a step of cooling the gas stored in said second gas tank using the ambient water when the underwater vehicle is in the submerged state within the water body where the temperature of the ambient water is lower than the temperature of the gas stored in said second gas tank. 
     
     
         6 . The method of  claim 1 , further comprising a step of heating the gas stored in said third gas tank using the ambient water when the underwater vehicle is in a submerged stated within the water body where the temperature of the ambient water is higher than the temperature of the gas stored in said third gas tank. 
     
     
         7 . The method of  claim 1 , further comprising a step of heating the gas stored in said second gas tank when said prime mover is in operation. 
     
     
         8 . The method of  claim 1 , further comprising a step of cooling the gas stored in said third gas tank when said prime mover is in operation. 
     
     
         9 . A compressed gas system for harvesting ambient hydrostatic pressure for an underwater vehicle operative to descend within a water body to a given depth and to ascend from the given depth in an alternating fashion, said system comprising:
 a first gas tank;   a second tank in fluid communication with the first gas tank;   a third gas tank in fluid communication with the second gas tank and the first gas tank;   a first valve for controlling a gas flow between the second gas tank and the third gas tank; and   a second valve for controlling a gas flow between the third gas tank and the first gas tank,   
       wherein gas stored in the third gas tank is selectively subjectable to the ambient hydrostatic pressure during a submerged state of the underwater vehicle within the water body. 
     
     
         10 . The system of  claim 9 , further comprising:
 a first differential valve operatively coupled to said third gas tank and configured to be selectively actuated when the ambient hydrostatic pressure is lower than the gas pressure in the third gas tank; and   a second differential valve operatively coupled to said third gas tank and configured to be selectively actuated when the ambient hydrostatic pressure is higher than the gas pressure in the third gas tank.   
     
     
         11 . The system of  claim 9 , further comprising a fluid decoupler interposed between and in fluid communication with said third gas tank and said first and second differential valves, wherein said fluid decoupler comprises:
 a piston defining a first and a second compartment in said fluid decoupler;   
       wherein said first compartment is configured to be in fluid communication with said first gas tank; and 
       wherein said second compartment is configured to be in fluid communication with said first and second differential valves. 
     
     
         12 . The system of  claim 9 , further comprising:
 a first heat exchanger configured to extract heat energy from the gas stored in said first gas tank; and   a second heat exchanger configured to transfer heat energy into the gas stored in said second gas tank.   
     
     
         13 . A method for pressurized electrolysis of fresh water in an underwater vehicle comprising the steps of:
 storing fresh water in a first water tank in the underwater vehicle;   pressurizing the fresh water in the said first water tank using the ambient hydrostatic pressure when said underwater vehicle is in a submerged state within a water body;   electrolyzing said pressurized water to release hydrogen gas and oxygen gas; and   storing said hydrogen gas and said oxygen gas in a first hydrogen tank and a first oxygen tank respectively.   
     
     
         14 . The method of  claim 13 , further comprising the step of cooling the stored hydrogen gas in said first hydrogen tank, thereby reducing the pressure of the stored hydrogen gas in said first hydrogen tank. 
     
     
         15 . The method of  claim 13 , further comprising the step of cooling the stored oxygen gas in said first oxygen tank, thereby reducing the pressure of the stored oxygen gas in said first oxygen tank. 
     
     
         16 . The method of  claim 13 , further comprising the step of heating the stored oxygen gas and the stored hydrogen gas in said first oxygen tank and said first hydrogen tank, respectively, thereby increasing the pressures of the stored oxygen gas and the stored hydrogen gas in said first oxygen tank and said first hydrogen tank respectively. 
     
     
         17 . The method of  claim 13 , further comprising the steps of:
 pressurizing the fresh water stored in said first water tank using the ambient hydrostatic pressure encountered by the underwater vehicle in the submerged state in the water body; and   transferring the pressurized water from said first water tank to a second water tank.   
     
     
         18 . The method of  claim 13 , further comprising the step of storing the hydrogen gas and the oxygen gas released in the electrolyzing step in a second hydrogen tank and a second oxygen gas, respectively, before storing the hydrogen gas and the oxygen gas in said first hydrogen tank and said first oxygen tank, respectively. 
     
     
         19 . The method of  claim 18 , further comprising the steps of:
 pressurizing the hydrogen gas and the oxygen gas stored in the second hydrogen tank and the second oxygen tank, respectively, using the ambient hydrostatic pressure in the submerged state of the underwater vehicle within the water body; and   transferring said pressurized hydrogen gas and said oxygen gas from said second hydrogen tank and said second oxygen tank, respectively, to said first hydrogen tank and said first oxygen tank, respectively.   
     
     
         20 . A system of pressurized electrolysis of fresh water in an underwater vehicle comprising:
 a first fresh water tank;   an electrolyzer in fluid communication with said first fresh water tank, said electrolyzer configured to electrolyze fresh water to release hydrogen and oxygen gases;   a first hydrogen tank and a first oxygen tank in fluid communication with said electrolyzer for respectively storing the hydrogen gas and the oxygen gas released by said electrolyzer; and   a first pressure transfer system configured to exert the ambient hydrostatic pressure on the fresh water stored in said first fresh water tank.   
     
     
         21 . The system of  claim 20 , further comprising:
 a first one-way differential valve interposed between said electrolyzer and said first hydrogen tank; and   a second one-way differential valve interposed between said electrolyzer and said first oxygen tank.   
     
     
         22 . The system of  claim 21 , further comprising:
 a second fresh water tank in fluid communication with said first fresh water tank via a third one-way differential valve, and with said electrolyzer via a first valve;   a second hydrogen tank in fluid communication with said electrolyzer via a second valve, and with said first hydrogen tank via said first one-way differential valve;   a second oxygen tank in fluid communication with said electrolyzer via a third valve, and with said first oxygen tank via said second one-way differential valve;   a second pressure transfer system adapted to exert the ambient hydrostatic pressure on the hydrogen stored in said second hydrogen tank, in the submerged state of the underwater vehicle within the water body; and   a third pressure transfer system adapted to exert ambient hydrostatic pressure on the oxygen stored in said second oxygen tank, in the submerged state of the underwater vehicle within the water body.   
     
     
         23 . The system of  claim 22 , further comprising a combustor configured to receive from said first hydrogen tank, the pressurized hydrogen gas, and, from said first oxygen tank, the pressurized oxygen gas for combustion therein. 
     
     
         24 . The system of  claim 23 , further comprising a heat transfer system configured to transfer at least some amount of heat, generated in said combustor due to the combustion of the pressurized hydrogen gas and the pressurized oxygen gas therein, to said first hydrogen tank and said first oxygen tank, thereby raising the temperatures and the pressures of the hydrogen gas and the oxygen gas stored in the respective first hydrogen and oxygen tanks.